Iselle, on track to pass over the Big Island of Hawaii as a Category 1 hurricane with winds of 80 mph, could bring up to 12 inches of rain, life-threatening storm surges, flash floods and mudslides, forecasters say.

Hurricane Julio, churning behind Iselle, could affect the islands two days later, though forecasters currently expect it to brush the state only with its outer bands as it passes to the north as a weakened tropical storm.

Customers picked through stores for groceries and other supplies Wednesday night. At many locations, such as KTA in Waimea, bottled water was sold out, leaving the seller scrambling to get more.

“We’ve been on the phone from very early (Wednesday) morning, working with our vendors trying to get more water. It’s been a very difficult situation because everybody is trying to get water,” store manager Colin Miura told CNN affiliate KGMB.

Flash flooding on already saturated islands will be a main threat, along with mudslides from some of the mountainous terrain into populated areas.

“Preparations to protect life and property should be rushed to completion,” the Central Pacific Hurricane Center said in its public advisory on Iselle early Thursday.

A hurricane warning was in effect for the easternmost populated island, Hawaii, with some of the state’s other islands — Oahu, Maui, Molokai, Lanai and Kahoolawe — bracing for tropical storm conditions, with sustained winds of under 73 mph.

A relatively rare event

Iselle would be one for Hawaii’s record books just by making landfall.

Direct hits are rare for the state. Since the 1950s, only two hurricane eyes have hit Hawaii — and both approached from the south, where water temperature generally is warm enough to sustain the storms’ strength.

Iselle, however, approaches from the east, and it would be the first tropical cyclone from that direction to hit the state since the satellite era began in 1959, CNN meteorologist Dave Hennen said.

That’s not to say Hawaii hasn’t had close calls. The central Pacific sees an average of about five tropical cyclones a year, and some have brushed the state in recent decades.

But Iselle is poised to overcome a number of factors that in recent decades conspired to keep the storms from hitting Hawaii directly or weaken them before they got there.

The cyclones generally approach from the east after forming in the eastern Pacific. But close to Hawaii, dry air, cooler water and wind shear combine to weaken approaching cyclones, dissipating them before they can become a significant threat, CNN meteorologist Indra Petersons said.

Now, however, the water off Hawaii is warmer than usual, and that could keep Iselle at hurricane strength if it hits Hawaii island as expected Thursday, Petersons said.

Hawaii’s most damaging hurricane in recent decades — Hurricane Iniki of 1992 — came during an El Nino year, or a year of above-average sea surface temperatures. This year hasn’t met the criteria for El Nino, but it could in the weeks ahead, Petersons said.

Iniki killed at least four people and caused about $2 billion in damage when it hit the western Hawaiian island of Kauai, according to the National Oceanic and Atmospheric Administration.

Storm dangers

Iselle should bring heavy downpours of 5 to 8 inches over the Big Island; in isolated spots up to 12 inches, the hurricane center predicts.

That could cause rock and mudslides.

Also, the storm surge could come on top of high tide, pushing 1-3 feet of water onto dry land, and depending on overlap with tides, could hit isolated areas hard.

Ports are taking no chance, and early Thursday, the U.S. Coast Guard upped warning levels to signal the the storm was nearing.

“All ocean going commercial vessels and ocean going barges greater than 200 gross tons are expected to make preparations to leave the ports,” it said in a statement. Ships wishing to remain in port are required to file a safe mooring plan.

Excitement and fear

In the town of Hilo on the Big Island, people were standing on beaches, anxiously looking out at the water.

“The surfers get excited about these storms, but everyone else is freaking out,” said Chris Owens, owner of East Side Builders and a longtime resident.

“A lot of the locals here believe that the tall mountains on the Big Island shield them from hurricanes,” Owens said. “But in 24 hours, this theory could be proven wrong.”

A National Weather Service map showed waves on islands west of the Big Island rearing up to heights of 10-15 feet. CNN’s weather center reported waves up to 40-feet high at Iselle’s location in the central Pacific on Wednesday.

That’s potentially good surf to Scott Murray, who owns the Hilo Surfboard Co. He has lived on the Big Island for more than 60 years. Many fellow residents are psyched about the waves and not concerned about potential damage and flooding.

“I’m not really worried about his storm,” Murray said earlier this week.

School’s out; elections still on

The schools on the Big Island and Maui will be closed Thursday as residents await Iselle’s arrival.

Some airlines are making concessions to customers ahead of the storms. For people who had been scheduled to travel to or from Hawaiian airports on Thursday and Friday, United Airlines and Hawaiian Airlines say they won’t charge fees to change reservations, and they’ll waive differences in fares for those changes.

Island Air will do the same for passengers ticketed from Thursday though Tuesday. Delta said it would waive fees for reservation changes for Thursday and Friday, but fare increases could apply.

Hawaii’s primary elections will go on as scheduled Saturday, despite the storms, KGMB reported. Local media reported that many turned up for early voting in expectation of severe weather on election day. Others are concerned that voter turnout could be affected.

Hawaii Gov. Neil Abercrombie has signed an emergency proclamation, his office said. It gives the government access to the state’s disaster funds.